In the past, various techniques have been developed for the purpose of sterilizing or decontaminating biological sludges and wastes. The most common process is the process of mixing lime with the sludge. The reaction of lime with the water in the sludge serves to elevate the temperature of the sludge for a maximum of 100.degree. C.
U.S. Pat. Nos. 4,781,842 and 4,902,431, issued to Nicholson, teach a process to decontaminate wastewater sludge to a level that meets or exceeds U.S. EPA process standards. The process mixes sludge with an alkaline material sufficient to raise the pH of the end product to 12 or higher for at least one day. This process will raise the temperature to 50.degree. C., but, will not sterilize the sludge, nor does it eliminate the pathogenic microorganisms.
U.S. Pat. No. 4,306,978, issued to Wurtz, relates to a process of lime stabilization of wastewater treatment plant: sludge. This patent discloses the dewatering of the sludge and intimately mixing calcium oxide to raise the temperature so as to produce a stabilized sludge particle.
None of these prior art inventions are capable of achieving temperatures, when mixed the sludge, of greater than 100.degree. C. None of these prior art techniques allow for the shorter drying times as required by 40 C.F.R. Subchapter 0, Part 503.32 a.311.A-D. The shorter drying times, as required by this Subchapter, are in accordance with the following formula: EQU D=131,700,000/(1.times.10**0.14t) (1)
where D=time in days t=temperature in degrees Celsius
Importantly, it is important to be able to treat biological sludge so as to kill off the eggs of parasites. Presently, a parasite known as helminth infects many people throughout the world. This is a parasite which crosses the blood/brain barrier so that the parasite can actually reside in the brain. Treatment has occurred in the past by simply chlorinating water so as to kill the living parasite. Unfortunately, tests have shown that the mere chlorination of water does not kill the egg of the parasite. If the egg of the parasite is delivered to a human host, then the egg can actually hatch within the human body and seriously infect the human host. Presently, there is approximately a thirty-six month life expectancy for those that are infected with the helminth parasite.
This is particularly a problem associated with municipal biological sludge. In certain areas of the world, the biological sludge of waste treatment processes is distributed in farming areas for use as a fertilizer on the field. If the municipal sludge contains the eggs of this parasite, then these eggs will reside within the field so as to ultimately be found on foods grown in the fertilized field. Furthermore, any water runoff from the field will tend to move the eggs from the field into a river or stream. In certain areas of the world, river or stream water is used for consumption and for bathing. As such, the eggs of the parasite can be delivered to such persons. Additionally, farm animals can often contact the parasite by consuming the water from the streams or by consuming food in the fields. It is possible for humans to become infected from the parasite by way of the eating of the meat of the animal. As such, it is very important to develop a process for the treatment of a biological sludge which effectively kills the eggs of the helminth parasite.
U.S. Pat. No. 5,635,069, issued on Jun. 3, 1997 to the present inventors, describes a process for treating a waste sludge of biological solids. This process is intended to decontaminate wastewater sludge to a level that meets or exceeds U.S. EPA standards. This process mixes sludge, under pressure, with calcium oxide and with sulfamic acid sufficient to raise the temperature to achieve pathogen destruction. Although the process is efficient with regard to pathogen destruction, it does not address process and economic advantages of adding or producing, during the process, ammonia, ammonium hydroxide or ammonium bicarbonate in a concentration of 200 ppm to 30,000 ppm. Furthermore, the product of the process of U.S. Pat. No. 5,635,069 has a relatively high pH. As such, the product of the process is not desirable for use as farm fertilizers until the pH is sufficiently lowered to a range of between 8.5 and 9.
It is an object of the present invention to provide a process for reducing biological waste sludge pathogen, bacteria, virus and parasite concentrations to below harmful levels.
It is another object of the present invention to provide a process that converts the biological waste sludge into a sellable and useable end product.
It is still a further object of the present invention to provide a process that eliminates or reduces waste incineration and landfilling of waste sludges.
It is another object of the present invention to provide a process that eliminates the odors resulting from lime stabilization.
It is still a further object of the present invention to provide a process that facilitates the dewatering of the biological sludge.
It is still another object of the present invention to provide a process that recycles waste heat.
It is still a further object of the present invention to provide a process for treating waste sludges that is cost: effective, easy to use, and easy to install.
These and other objects and advantages of the present: invention will become apparent from a reading of the attached specification and appended claims.